Remove the <Interval> from opendnssec conf
    
    In opendnssec 2.1.6, the <Interval> element is not supported in the
    configuration file.
    
    Related: https://pagure.io/freeipa/issue/8214
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>